Photographic emulsions containing nu-aryloxy-, arylthio-and arylselenoalkyl cyanine dyes



Sept. 6, W49. rA. W. ANlsH EMULSIONS CONTAINING N-ARYLOXY- PHOTOGRAPHIC ARYLTHIO- AND ARYLSELENOALKYL CYANINE DYES 4 Sheets-Sheet 1 Filed Dec. 29, 1945 Sept. 6, 1949. A. w. ANlsH 2,481,454

PHOTOGRAPHIC EMULSIONS CONTAINING N-ARYLOXY,

ARYLTHIO- AND ARYLSELENOALKYL CYANINE DYES Filed Dec. 29, 1945 4 sheets-sheet 3 Jill/81%)@ A Mr/zeg Sept, 6, 194:9o A. w. ANlsH 2,481,454

PHOTOGRAPHIC EMULSIONS CONTAINING NARYLOXY, ARYLTHIO- AND ARYLSELENOALKYL CYANINE DYES Filed Dec. 29, 1945 4 sheets-sheet 4 O4 O I- Patented Sept. 6, 1,949

2,481,464 PrroToGRAPnro EMoLsioNs coN'rAi'ri-Ne AND ARYL- SELENOALKYL CYANINE DYEs Alfred W.,Anish, Vestal, N. Y., assignor 'to eral Aniline & Film Corporation, New York.

N. Y., a corporation of Delaware Appiieatien December 29, 1945,s1ena1 Nei 638,493

4 Claims.

This invention relates to new cyanine dyes and to vphotographic emulsions sensitized by such dyes.

It is well known that the type of group attached to the cya-nine nitrogen atoms in cyanine dyes exert an influence on the properties of the dye. For example, it hasbeen l'nown for some time that where there is an'alkyl group on the cyanine nitrogen, the maximum Vintensity of sensitization'is reached With the ethyl or propyl group and that the sensitization decreases When the number yof carbon atoms ih the alkyl group is increased.

other substitutions menthe alkyl group have been proposed. For example, in U. S. P. 2,231,658, there'are disclosed cyanine dyes Ahaving an oxygenn eontainivrig aikyi g'riip devoid of aryl substituents such as, fr instance, alkox'y alkyl, 'hydroxy alkyl, the halogen-'containing and cyanogene'centaining alkyl-groups. The dyes 'proposed in this patent provides'e'nsitizers for the red, far-red and infrared and increase the 'solubility 'of the dye which iii turn minimizes residual 4dye stain ollov'ving photographic development.

Aceording to my invention, I have found that the introduction of aryloxyalkyl, 'arylthioalkyl and arylselenoalkyl groups o`n at east one of the two cyanine nitrogen .atoms of certain yanine dyes 'provides new dyes having highly desirable preperties;

The 'cyanine dyes coming within the scope of my invention are those in which one of the heterocyclic nitrogennuclei is Aselected from the group consisting or '5- -andG-membered heterocyelic nitrogen nuclei and the other is a y5-mem' bered heterocyclic nitregen nucleus.

VTl'ie dyes `eoiiip'rising my' invention may be represented by the following general formula:

rije-(M) ..=-i\I-Rl X- Wl'ierein Y represents the non-metallic atoms necessary to complete av heterocyclic nucleus of the 5- and f-memloeredheterocyclic nuclei; Z represents the non-metallic atoms necessary to complete a -membered heterocyclic nucleus; M represents .a methenyl chain; n represents a positive odd integerA such as 1, 3, 5, 7, 9, and 11,; X an acid group; R and R alkyl, aryl, aralkyl, cycloaliphatic, at least one of the Rs being a -(CHi) m--A- aryl group, wherein m is a positive integer such as 2 or 3, A represents O, S, or Se, and aryl represents Yan -aryl group of the benzene and naphthalee series. More particularly, the dyes may be represented by the following formulas:

reicance 'as in Formula I.

IIJiore particularly, in the labove formulas, Y, for example, represents the non-metallic atoms necessary to complete a heterocyclic nucleus as, ier instance, 1a member of the oxazoie series, e. benzoxazole and naphthoxazole; a member of the thiazole series, e. =g. benzt-hiazole; a member of the thia'zoline series, e. g. thiazoline; a member of the pyridine series, e. g. pyridine; a member `of the 'quinoline series, e. g., benzoquinoline 'or quinoline; a member vof the selenazolel series, e. g. beiizselenazole; a member of the selenazoline series, e. g. selenazoline, or a member of the indolenine series, e. g. 3,3-dimethyl indolenine.

More particularly, Z represents, for instance, the non-metallic Vatoms necessary to complete a 5membered -heterocyclic nucleus, such as of the thiazoline or selenazolin'e series, e. g. thiazoline or selenazoline; of the thiazole series, e. g. benztln'iazole; the oxazole series, e. g. benzoxazole; of the selenazol'e series, e. g. benzselenazole; of the indolenine series, e. g. 33-dimethyl indolenine.

More particularly, .n is a positive odd integer, for instance, not greater than Al1; m is a positive integer as, -for leii'ftmp'le, 2 or 3, X is an acid group as, for siam-ple, chlorine, bromine, iodine, metlrisul'fate, para-toluene, sulOn'ate, perchlorate, fete. Aryl may be "benzene or naplqthalene or chloro-benzene or phenyl substituted, for eX- ample, .by methyl methoxy or a branched aliplatic 'eiai-n, as' dii-isopropyl, di-isobultyi, tertiaryebutyl or' by yloliiryh R and R may be, for example,- i'r'iethyl, ethyl, isopropyl, allyl, -'eth'oxyeth'y'l, vfylohe'iyl, phenyl, 'etc'.

Mgr' nevv 4dyes have vmany advantages and novel properties. For eiai'rple, itis often necessary to increase the molecular bulk of a dye for purposes vo'f non=diffusion- Howevensuch increase in molecular size /'f 'the 'eyaniiie dyes by means of increasing the molecular size of the alkyl lor araikyi Lgreups feyar'iiiie nitrogen atterrisjef heretofore ya-nine dyes 4din'iinislfles the @veran power of' seiis'itiiatin. Thus, substitutlng the ya-ine iiitogerl aralkyl group in the aryl Ytutions in the aryl portion of, the molecule.

Thus, alkyl, branched alkyl groups, phenyl, cyclohexyl and halogen, such-as bromine and chlorine groups may be substituted in the aryl portion of the dye molecule without materially alecting the speed or power of sensitization of the dye.

Another advantage vof the dyes of the present invention is that they do not wander or diffuse when they are utilized in multilayer photographic coatings such as are employed in color photography. Nor are they displaced from the layer by the color former that may Ibe present. This and lother unique properties of my new dyes make them highly valuable in the photographic arts.

My newdyes can lbe readily prepared from cyclammornum quaternary salts, the preparation of which will be presently described. In general, these salts may be referred to as cyclammonium aryloxyalk'yl, arylthioalkyl vand arylselenoalkyl quaternary salts. They can, in general, be prepared by reacting a heterocyclic nitrogen base with an aryloxyalkyl, arylthioalkyl, arylselenoalkyl toluenesulionate. The preparation of such toluenesulfonates is generally effected by reacting -p-toluene sulfonyl chloride in the presence of a base such as caustic alkali, or pyridine with an Varyloxyalkyl alcohol, aryltlnoalkyl alcohol or arylselenoalkyl alcohol. The method of preparing such p-toluenesulfonates is illustrated by the following examples: Y Y

EXAMPLE 1 p-(t-butyl) phenoy ethyl p-toluenesulfonate 19.4 grams (0.1 mol) of -(p-tertiary butyl phenoxy) ethyl alcohol were dissolved in 32 grams of pyridine and 20.9 grams-(0.11 mol) of ptoluene sulfonyl chloride were added while stirring. The temperature was kept below 5 C. while adding the latter reagent and the stirring Was continued for an additional 3 hours at a temperature under 2GD C. After standing for 12 hours, the reaction solution was poured into 60 cc. of concentrated hydrochloric Vacid .diluted with 140 cc.`of water. The white solid Vrwas liltered off, Washed with 2 N caustic alkali solu- .tion and finally with cold water. Y After drying,

the solid was recrystallized -from petroleum ether B. P. 90-100 C. The product had Ia melting point of 92 C.

In a similar manner, p-di-isobutyl phenoxyethyl p-toluenesulfonate was prepared and had a melting point of 86 C. Similarly, there was prepared .p-methyl phenoxyethyl p -toluenesulfonate, which melted :at 55 C., p-cyclohexyl phenoxyethyl p-toluenesulfonate which melted at 113 C., p-chlorophenoxyethyl p-toluenesulfonate which melted at 70 .C'., fand' p-phenyl phenoxyethyl -p-toluenesulfonate which melted at 152 C. l

The aryl thioalkyl and arylselenoalkyl 4p-toluenesulfonates are prepared by reacting :thioor seleno-phenol or substituted thiophenol or selenophenol with chlorohydrin in the presence of 4 1 sodium -alcoholate and' then 'reactingV the aryl thioalkyl or aryls'elenoalky-l alcohol with p-tolu- K. ene sulf-onyl chloride in a similar manner as illustrated in Example 1.

sture.

siredcan readily be converted into the Varyloxy-Y Illustrative of the method of preparing the cyclammonium l aryloxyalkyl, arylthioalkyl and arylselenoalkylV quaternary salts are the following examples: Y

EXAMPLE 2 Z-methylbenzth'iaeole phenoyethyl p-toluenesulfonate Equal parts Iby weight of 2methylbenzothi azole and .phenoxyethylf p-toluenesulfon-ate were heated .together in an oil 4bath at 13G-140 C.V for 16 hours A mixture vof dryv acetone and dry ethyl ether was added to the cooled reaction mix-gi.V

rubbing The. 'crude thick oil solidified on and was used in thel preparation of` dyes. EXAMPLES V ylthz'oethyl p-toluenesitlfona'te 2-pzetyz-aci-methylenedioy benzthideoze phen-i Equal parts bye/eight of,phen'y1thioet1-1y`1ptqli uene-slufonate and 2-methyl-5,6-methylenedioxy'yv benzthiazole were heated 12 hours at 13G-'140 andA then washed with ainixture'of ydry ether and dry acetone. rThe residue was usedwithoutfurther purification for the preparation of dyes. Y

In a similar manner tethat'iuustrated, zlmethylbenzoxazole, 2-methyl-S-methoxy-benzselenazole, 2-methyl-6,7-benzobenzthiazole, 2-methyl-4- phenylthiazole, 2-methyl -4 phenyloxazole, ,2-1, methyl-e-phenylselenazole, 2-methyl thiazoline, Z-methylmercapto benzthiazole, Z-phenylmercapto benzthiazole, for. instance, can be converted into the aryloxyalkyl, arylthioalkyland arylselenoalkyl quaternary salts. i By usingl 'p-dilisobutyl phenoxyethyl p-toluenesulfonate, p-methyl phenoxyethyl p-toluenesulfonate, p-cyclohexyl phenoxyethyl p `toluenesulfonate, p-chlorophenoxyethyl p-toluenesulfonate, p-phenyl phenoxyethyl p-toluenesulfonate and the corresponding sulfur and seleno compounds, the corresponding. arylox'y--fy alkyl, arylthioalkyli and, arylselenoalkyl quaternary saltswhi'ch are substituted in .thearylnucleus are obtained. y 'The toluee sulfonate quaternary salts, if de'- n alkyl, arylthioalkyl, and arylselenoalkyl halides or perchlorates, by treating solutions vof the aforementioned toluenesulfonates with solutions of s01- uble'halides or'perchlor'ates, such as, potassium iodide or bromide or sodium perchlorate.

The intermediates 'described "may be readily Y employed inv preparing Vsimple-*cyaninal carbocyanine, dicarbocyanine, tricarbocyanine, tetra and pentacarbocyanine dyes, hemi-cyanines, vstyrylV dyes, and dye bases.

` The following examples will serve to illustrate the Various methods of obtainingthenew c'yanine dyes but are not intended to limit the invention.v

' n vEXAMPLE V4 A H I Y acc-:gm:

2.5 grams of a'methyieoemethcxy -ueriiisolena.- Zele phenoxyaethyl petoiuenesuifcnate `and i197 grams mmethylmercapto-G-methyl duinoline `ethiiedide were `dissolved in 100.0 cc. if-absolute ethyi alcun-o1 and d2.o cc. of ftrietnyiamine added. The

tion produc'twwas 'nitered while 'stili Thot-and 'the crystals which separated onc'ool-i'n'gwere riecrysi tallized from methyl alcohol. Instead of employing .the 2-methylmercapto-6-methyl quinoline ethiodide, the cor-responding 2-iodointermediate may be employed to prepare the dye.

When coated lin combination with chain Suhl stituted panchromatic dyes the speed 'of 'the 'r'esulting emulsion was greater than of either dye coated alone. The dye from Example 4 acts as a dye-supersensitizer. For example, 25.0 milligrains of dye from Example 4 and 40 milligrams 3,3-diethyl-9-methyl benzthiocarbocyanine iodide perkilogram of emulsion were coated in a 4-5% silver halide gelatin emulsion containing silver bromide and silver iodide. The speed of theresulting emulsion was' at least one stopfaster under aminus plus filter than either dye used alone.

T he dye sensitizes with a maximum at 550 mu to ssornu.

Eamonn 5 CiHi Y Mei-cw CH- \II N CiHl ((H 2.0 grams each of 2-(-ani1ino-p-ethyl vinyl) G-phenyl benzoxazole ethiodide and 2-methy1 benzthiazole phenoxyethyl p-toluenesulionate were reuxed 2 hours in 10 cc. of gpyridine. The mixture was cooldand diluted withlO cc. water containing 1.0 gram of potassium iodide. The dye crystals which separated on standing were recrys'tallized twice lfrom ethyl alcohol. The sensitivity of the dye extends to 600 mu with a maximum at 570 mu. Y

- EXAMPLE 6 o s i Hao carbon-@Efo 1 f. i I- i.8 grams o'f ".2-methyl-5,6-methylenedioxy benzthiazole pechloro phenoxyethyl p-toluenesulfonate and 3.0 cc. of ethyl o-formate in 15.0 cc'. Iof pyridine were reiluxed for 3 hours. The reaction mixture was diluted with an equal yoluIe of 95% :ethyliaicohola-ndrlet stand. Tlieiiye e. methyl alcohol. The d?" 'iiv converted to the iodide by redissolving the puried dye in 95% ethyl alcohol and adding 10% potassium .iodide solution. The sensitivity of the 'dye extends to 680 mu with a maximum at 640 mu.

EXAMPLE 7 mu with a. maximum at 640 mu.

EXAMPLE 8 C-C HIC H-CHIC 1.1 'grams of2 -methyl-5,6-methylenedioxybenzthiazolef-(p-di-isobutyl) phenoxyethyl p-toluenesulfonat'e and 3.0 cc. of ethyl o=fformate were mixed .ii1v 15;0 cc. of pyridine and lieatedr21/2-3 hours. The pyridine solution was diluted with an equal volume of ethanol and precipitated as the iodide with potassium iodide.

When incorporated into a silver bromide-silver iodide gelatin "emulsion in a concentration of 40 milligrams per kilogram of emulsion, the dye had a strong sensitivity with a maximum at 640 mu and sensitivity to 680 mu. The dye did not diffuse which :crystallized @out was recrytalldd from, 15 in multilayei'eotings.

i annee-.s

1. 7 grams of 2methy1-5,6-methylenedioxybenzthiazole (1a-methyl)"iphenoxyethyl p-toluenesulfonate and 3.0 cc. of 4ethyl o-formate were mixed in 15.0 cc, of pyridine and heated to reux 21/2-3 hours. The dye was recovered as"the bromide in a manner similar to that described for Example 8. The dye sensitized with a maximum e -.2 .0 "grams'oi'2-methy1 benzthiazole phen-ylthioeth'ly; lp-.toluenesulfonate VAwere mixed withV 3,0 cc.

otethylo-formate in 20.0 cc. of pyridine and rer, luxed. 21: hoursg.- `The dye which separated on Y standingswas ltered off .andrecrystallized from methylalcohol. WThe dye was redissolved in alcov hol and-precipitated as the iodide. The dye sensi-f tized to 680 ymuqwitha maximumat .640 mu.; 3

- r. Ensim "2.0 grams Ycif 2Lmethyl45,6methylenedioxy benzthiazole-(p-methoxy) phenoxyethyl p-toluenesulfonate were mixed Vwith 3.0 cc. of ethyl oformate and refluxed in 20.0 cc. ofV pyridine for 21/2-3'hours. The'dyevwas isolated as the bromide Y salt 'and puriedjust as inv Example 8. The dye sensitized to 680 mu with a maximum at 640 mu.

y EXAMPLE 13 benzthiazole-(-naphthoxy) ethyl" 'ptoluenel sulfonate were reacted with 3.0 cc. of vethyl oformate in 20 cc. of pyridine in a manner similar i The dye was isolated as: the chloride. The dye sensitized to 680 :nun

tou thatv for .Example 8.

9 thioethyl p-toluenesulfonate were dissolved in 15.0 cc. of pyridine and reacted in the presence of 1.0 cc. of thiethylamine. The dye was recovered and puried in a manner similar to that of Example 8. The dye sensitized to 680 mu with a maximum at 640 mu.

Z.3 grams o! 2methyl5,6-methylenedioxybenzthiazole phenylselenoethyl p toluenesul- Ionate and 5.0 cc. of ethyl o-formate were mixed in 25.0 cc. of pyridine and heated for 21/2-3 hours to reux. The dye was redissolved in methanol and reprecipitated as the iodide. The dye sensitized to 680 mu with a maximum at 640'inu.

EXAMPLE 1'6 the accompanying drawing illustrate the regions o the spectrum to which the various N-aryloxy, ai'ylthio- ,and arylselenoalkyl dyes ldisclosed herein will sensitize va vgelatino silver-halide emulsion and the extent of the sensitization at various wavelengths. The thirteen gures of this drawing illustrate the sensitiaing properties of the dyes in silver-halide emulsions in accordance with the present invention.

Figs. 1 to 13 inclusive illustrate the sensitizing properties of the dyes of Examples 4 to 16'inelusive.

The dicarbocyanine dyes containing aryloxyalkyl, arylthioalkyl, arylselenoalkyl groups 0n at least one of the cyanine nitrogen atoms can be prepared by condensing (1) a cyclammonium quaternary salt having one of the aforementioned groups on the nitrogen atom and containing a reactive methyl group with (2) the same or a different cyclammonium quaternary salt containing in a reactive position a 4- acetanilidobutadienyl group. Or, the compound (1) may contain the 4-acetanilidobutadienyl group in a reactive position instead of a methyl group and compound (2) a methyl group in a reactive position instead of the 4-acetanilidobutadenyl group.

The tricarbocyanines can be prepared in a similar manner, except that compound (1) or (2) carries in a Yreactive position the acetanilido hexatrienyl group, the other compound yhaving a reactive methyl group.

Compounds containing the 4-acetanilidobutadienyl group in a reactive position and having an aryloxyalkyl, arylthioalkyl, or arylselenoalkyl group in the nitrogen atom can be prepared by condensing the corresponding cyclammonium quaternary salt having a methyl group in a reactive position with -anilinoacrolein anil hydrochloride, in the presence of acetic anhydride. When the condensation is carried out with glutaconic aldehyde dianilide hydrochloride, the corresponding cyclammonium Quaternary salt having an acetanilido hexatrienyl group in a reactive position is obtained.

The following examples will serve to illustrate the preparation of dicarbocyanine and tricarbocyanine dyes.

EXAMPLE 17 Equimolecuiar amounts of Z-(Ll-acetanilido- :butadienyD 5,6 methylenedioxy benzthiazole ethiodide and 2-methyl-5,6-methylenedioxybenzthiazole phenylthioethyl p-toluenesulfonate were condensed following the same procedure as Example 14. A dye was recovered having Vthe Vfollowing formula:

Y aboutV moisV are preferable. The condensing VV35 Vsalts are utlhzed 1n equimolecular amounts al- Y R1' algarv l EXAMPLE 18 e Vemulsion'withjstirringjin Ilthe dyeisltliorfiu` i When equimolecular amounts of-"Z-(G-acet- 1y neorperaree rheremf f Y e, aniiieohexatrienyi) 5e:methyienedicxybena If deslred, the dye may bencorpfteelw thiazoie emmerde and 2-methy1-5-methy1ene Othelmethods- Thuathe photveraphicemulslerr dioxybenzthiazoie phenyloxyethyi p-to1uene- 5 Coated 0n a suitable support, as a lm-Or plate, sulfonate are condensed following the procedure may be bathed with a solution of the dye in of Example 14, a tricarbocyanine dye was re-Y an appropriate solvent-iiV However, the aforecoveredV having the following formula; o 1 mentioned method is theV preferred one,

o\ ,/s; ,l I si /sV /o' roo/ ofon=Cn-oH=oH-oH=CH- 3H=o\ \Q/d a 'f It 02H5 toner As condensing agents for preparing the new I claimsY t f dyes, in addition tothe pyridine and triethyl- 1. A photographic gelatinersilvr-halideeinule Y amine mentioned in the above examples,l any sion which contains a vdye selected from the group other suitable condensing agents may be utilized, Y 'consisting oi' .dyes of thergenera'l'formulaer,zer such as dimethyl pyridine, ethylpyridine, ethyl M f 5. f Y r methyl pyridine', tribut'ylamine,'triethanolamine 3`0 Y s n es sodium or potassium carbonate, etc. In general, N (CH=CH)M CLCHzwHgCmPFC/ 'ether amountY of condensing agentv utilized .may e f vary within Wide limits, e. g. from 1 to 25'mols. Concentrations ranging efromeabout .1 Ymol to` I l; j

agentsmay-'also serve as diluents, but other and u diluents, such as, methyl, ethyl, n-propyl and ,z ,1.V ';o2H-- .z,` iso-propyl alcohols are advantageouslyemployed \C CH=C CE=C lin the condensation reactions.,V n l Y In general, the cyclammonium quaternary Vthoughrgreater amounts of eithermay be em- 'and arylselenoalkyl toluenesulfonate Quaternary 60 V0 Y s' s Y Vs vsalts may Ybe converted into theV halide and Y employed in the condensation reactions tokform i Yployed. Heating facilitates the reaction and the Wherem R' rerresenrs'a member sel-eeted from reaction is carried out readily at reiluxing temv the dass eorlslstmg of alkyl aralkylfaryloxy' peratures. f Y Y Y, Y i Y Y 45 alkyl, arylthioalkyl and arylselenoalkyl groups,

In the above exemples Where ethyl ert'hofep Rirepresents a member selected fromlthe class mate is employed, other esters of Yorthoformic Consisting 0f `ilfylOXyalkyl, arylthioalkyl and acid may be Yutilized instead. There may be afrylselenealkyrgreups "rrr Yr-erlresentsf;e'.v positive also employed in the above examples ethyl orthornteger er irre-m 1 to 2mn -frepresevnts' ai .Feen-rye acetate, 'ethyl orthopropionateY and ethyl ortho- 50 Integer 0r rrm;v lyre e' X represents err' aerd benzoate instead of ethyl orthoformate In such radcleiY represents'the aOmS HBCSSSaIy t0 comcases, the central carbon atom of the trlmethenyl were a member selected frem'r'he elasseensrsrmg chain of the dye will Ibe substituted by an ethyl, e er 5'membered and emembered' hetereeY-Clie propyl and phenyl group, respectively. Instead nrrogeneurs ring system and Z represents 'gehe of forming the dye by use of the toluene sulfonate atoms necessary "ro complete .la ,emembered cyelammonium Quaternary salts and then conhetereeyelie nitrogeneus rfmg sysremverting the resulting dye salt Vto the'chlorine, 2' A photographle gelatmor'sllver'hanede-emul' bromine, iodine or perchlorate dye salt, asl in the 'Sion eonteming'thefrouewingdyez Y' l above examples, the aryloxyalkyl, arylthioalkyl i perchlorate salts as indicated above and these H20' "o'oH=oH-ofH="- on? the dyes. Y Y Y ,0 t

In the preparation of,photographiceemulsions El HI sensitized with my new dyes,l Vthe dyesrmay be Y dissolved in methyl or ethyl alcohol anda volumev J) of this solution containing from 5 to 50 milligrams of the dyeadded to a kilogram of emulsion: 5

The emulsion isany of the usually employed silver halide emulsions, as for example, the silver chloride and silver bromide type with gelatin as the carrier, although any other carriers may re- C C place the gelatin such as cellulose derivatives or resins. The solution of the dye is added to the otllom o C|1\ sion containing the following dye:

sion containing the following dye:

ALFRED W. ANISH.

14 REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENT? Number Name Date 2,075,153 Wilmanns Mar. 30, 1937 2,213,238 Brooker et al. Sept. 3, 1940 2,213,995 Riester et al. Sept. 10, 1940 2,231,658 Brooker et al. Feb. 11, 1941 2,231,659 Brooker Feb. 11, 1941 2,233,511 Brooker et al. Mar. 4, 1941 2,235,027 Kumetat et al. Mar. 18, 1941 2,238,231 Riester et al. Apr. 15, 1941 2,256,163 Kumetat et al. Sept. 16, 1941 2,289,300 Wilmanns et al. July 7, 1942 2,354,524 Kumetat et a1. July 25, 1944 2,398,999 Brooker et al. Apr. 23, 1946 OTHER REFERENCES Chemical Abstracts, 19: 530; abstract of Proc. Roy. Soc. (London) 96 B. 317-333 (1924).

Chemical Abstracts 16: 3101; abstract of Brit. Med. JOurnal, 1922 I, 514-515. 

